What is Multipath Error and How It Degrades GPS Accuracy
A GPS satellite signal travels roughly 20,000 kilometres to reach a receiver on the ground. On that final stretch, near the ground, the signal can bounce off buildings, water surfaces, vehicles, or even dense foliage before arriving at the antenna. This bounced, delayed arrival is called multipath error, and it is one of the most persistent accuracy problems in real-world GPS survey work, particularly in urban and industrial environments.
How Multipath Actually Corrupts a Position Fix
A GPS receiver calculates position by precisely timing how long each satellite signal took to arrive. A direct signal path gives an accurate timing. A reflected signal path is longer than the direct path, arriving slightly later, which the receiver may mistakenly interpret as extra distance to that satellite. This false distance measurement pulls the calculated position away from the true location.
Where Multipath is Most Severe
Surveying near tall structures like this requires extra care, since reflected signals here can silently corrupt an uncorrected position fix.
How Survey-Grade Equipment Fights Back
Multiple satellite signals converging on a receiver behave somewhat like this network, except reflections introduce noise into the connections.
Practical Field Strategies
| Situation | Recommended Approach |
|---|---|
| Urban construction site survey | Use Total Station for critical points near buildings, DGPS for open areas |
| Reservoir shoreline survey | Position rover away from open water edges when possible during static observations |
| Industrial facility mapping | Increase occupation time near large metal structures for averaging benefit |
Our field crews recognize multipath-prone environments and adjust method and equipment accordingly, ensuring reliable accuracy even in challenging urban or industrial settings. Learn more about our DGPS and RTK survey services.
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